About 70% of the surface of the earth is water that is predominantly oceans. Accordingly, no matter how human culture and technology develop, mankind is extremely dependent on the ocean. Many governments' current ocean policies emphasize issues of ocean traffic safety, rescue at sea, fishery resources management and so on.
A ship's log traditionally provides a full nautical record of a ship's voyage including location and speed of the ship, observations from the ship and events occurring on the ship. However, most ship's logs are not useful immediately in effecting a rescue when a ship accident occurs because the ships' logs are aboard ship rather than in the hands of the rescuers.
At present, three systems are used for rescue on the ocean and include the Global Maritime Distress and Safety System, the Ship Security Alert System and the Automatic Identification System (AIS). When a ship meets with misfortune, the three systems send out emergency distress signals through the Global Positioning System (GPS), and the rescue is executed in the area where the emergency distress signals are transmitted.
Because the GPS is extremely expensive to use to report a ship's position, most ship companies cannot afford to transmit signals frequently via GPS. The late known position at the receiving end is not the same as the position of the ship at the time of an accident, so there are often great mistakes in rescue on the ocean, such as delayed rescue, incorrect rescue areas, etc. Research related to AIS by Lloyd's Register indicates that AIS often has insufficient messages about the destination, speed, direction and so on of a specific ship at a specific time to adequate determine the ship's position. Insufficient messages are often the key factors leading to inefficient rescues on the sea.
U.S. Pat. No. 6,778,809 B2 published on Aug. 17, 2004 titled “Mobile Network for Remote Service Areas Using Mobile Stations” disclosed a system and method for transmitting and receiving data in a mobile communication network. The system includes one or more mobile stations for transmitting data in a mobile digital network. The mobile stations are configured to act as buffer/repeaters by storing and forwarding data signals until they are received by a specific destination station. A relay means is utilized in the system to form the mobile network. However, the distance from one station to an adjacent station in an international shipping route is usually too far for the ships to effectively communicate. The relay means has the following problems    1. The data origin is too far away from the destination resulting in an excessive hop count, and the communication efficiency decreases when the relay count increases.    2. All the stations in the shipping route are not connected to other ships all the time so communication is often intermittent.
Based on the foregoing problems, once the data signals received from a ship meeting with misfortune are not sufficient to identify a ship's accident position. Finding a way to obtain a correct position for a ship's accident is urgent required to affect timely rescues.